Embodiments described herein relate generally to ventilation of a combustion engine. More specifically, embodiments described herein relate to reduction of blow-by gas coking in a closed ventilation system of a combustion engine.
During operation of a combustion engine, gas is pressed out of the combustion chamber and into a crankcase through a gap between a piston ring and a cylinder wall. Gas may also come from valve stem seals and turbocharger seals. This oil entrained gas is called blow-by gas. Unless removed from the crankcase, the blow-by gas increases the pressure inside the crankcase.
Conventionally, the blow-by gas may be vented from the crankcase with a crankcase ventilation system, also called a breather assembly. In an open ventilation system, the breather assembly vents to the atmosphere, however blow-by ventilation to the atmosphere is considered part of a vehicle's total emissions. For this reason, emission of the blow-by to the ambient is usually avoided.
Another conventionally known crankcase ventilation system is a closed breather assembly, where the blow-by gas may be vented back to the engine, for example by first being vented to a turbocharger compressor. Venting blow-by gas to the engine intake/turbocharger compressor inlet can potentially contaminate the air intake hardware of the engine/turbocharger compressor. Under high temperatures, the oil entrained in the blow-by gas can harden and stick to the engine/turbocharger compressor. The hardening and sticking process of the oil from the blow-by gas is known as coking.
Another known method of venting the blow-by gas is forcing the blow-by gas into the exhaust gas so that both emissions are treated by an aftertreatment system of the vehicle, for example either a diesel oxidation catalyst (DOC) and/or a diesel particulate filter (DPF). To inject the blow-by gas into the exhaust, the blow-by gas must be heated and compressed so that the blow-by gas can remain in a gas phase. Additionally, the entrained oil may deposit on the DOC and cover the active sites of the catalyst, which may lower the effectiveness of the aftertreatment system, for example by lowering levels of passive DPF regeneration and increasing the light-off temperatures needed for active DPF regeneration. Alternatively, the blow-by gas emissions may result in higher rates of ash accumulation at the DPF, which may require more frequent ash removal servicing.